1. Field of the Invention
The present invention relates to blends based on vinyl-aromatic polymers having high tenacity and impact strength.
More particularly, the present invention relates to blends of vinyl-aromatic polymers having high tenacity, suitable for producing shaped articles endowed with good impact strength properties.
2. The Prior Art
As known, the vinyl-aromatic polymers in question are prepared by polymerization, either in mass or mass-suspension, of solutions of polybutadiene rubbers or styrene-butadiene rubbers, or saturated rubbers of the ethylene-propylene type, in a styrene-acrylonitrile mixture. The resulting polymer is suited to the production of molded or extruded articles having a fairly good tenacity, which is sufficient for normal uses but insufficient for those applications, in which a high impact strength is required.
This is due to the fact that by said polymerization procedure (other than the polymerization in emulsion generally utilized for the production of the ABS resins) it is possible to employ only reduced amounts of rubber, owing to the too high viscosities of the polymerization mass.
A way to overcome this lack of properties is that of preparing blends with other polymers which possess the lacking properties, to obtain a material exhibiting the desired combination of properties. However, this approach was successful only in a few cases: generally, in fact, the blending results in the combination of the worst characteristics of each component, so that a material with so poor properties is obtained, that is it has no commercial or practical value.
The reasons for this drawback depend on the fact that not all the polymers are compatible with one another, and therefore they do not perfectly adhere. This gives rise to interfaces between the components of the mixture, such interfaces representing the weak and break points.